Generally, polyimide resins are manufactured through condensation polymerization of aromatic tetracarboxylic acid or its derivatives and aromatic diamine or aromatic diisocyanate, and thus manufactured polyimide resins have superior heat resistance, chemical resistance, mechanical and electrical properties. Photosensitive aromatic polyimides having such superior properties are widely used for electronic materials such as semiconductor encapsulant, etc.
However, aromatic polyimides are not appropriate for transparent protection layers or insulation layers for liquid crystal display devices in that they have low transmittance in the visible region, are colored in yellow or brown, and have a relatively high dielectric constant. Epoxy resins or acrylic resin compositions have been widely used as transparent protection layers or insulation layers for liquid crystal display devices. But their inherent heat resistance characteristics practically limits subsequent processing condition to below 230° C. When they are processed at temperatures of 250° C. or higher, severe decoloration and film contraction may occur.
Accordingly, polyimide materials have been taken into consideration in order to meet heat resistance and transparency simultaneously, and some methods of manufacture of polyimides by using alicyclic acid anhydrides have been reported as studies for obtaining transparent polyimide membrane or film (Macromolecules, 1994. 27, 1117 and 1993, 26, 4961, Japanese Patent Laid-Open No. PYUNGSUNG9-95533, Japanese Patent Laid-Open No. 2001-330721).
However, in order to use such non-photosensitive transparent polyimide resins as protection layers or insulation layers for liquid crystal display devices, the process of minute pattern formation by lithography process should be added after polyimide film formation on substrates composed of glasses, etc.
While the use of photosensitive transparent polyimide resin compositions is advantageous in view of cost reduction since the above-described process can be simplified, the photosensitive transparent polyimide resin composition using trans-1,4-diaminocyclohexane reported in Japanese Patent Laid-Open No. 2002-161136 is practically inapplicable due to too slow photosensitivity.
The inventors of the present invention has reported photosensitive transparent polyimide resin compositions in Korean Patent Application No. 10-2002-074070 leaving the development margin and photosensitivity to be improved further.